Apparatus for sensing physiological potentials

ABSTRACT

Apparatus is provided for sensing physiological potentials of a living body. There is provided a first band for at least partially encircling a part of the living body and having a first electrode mounted thereon. The first electrode is adapted for connection to an instrument for amplifying the physiological potentials of the living body. A second band is provided for at least partially encirling another part of the living body and has a second and a third electrode located thereon. The second and third electrodes each are adapted for connection to the instrument for amplifying the physiological potentials of the living body.

United States Patent [191 Raddi et al.

[111 3,826,246 [451 July 30,1974

1 1 APPARATUS FOR SENSING PHYSIOLOGICAL POTENTIALS [75] Inventors:William J. Raddi, Philadelphia;

Robert William Johnson, Levittown,

21 App]. No.: 337,262

[52] US. Cl. l28/2.06 E, l28/2.06 B, l28/DIG. 4 [51] Int. Cl A6lb 5/04[58] Field of Search 128/206 E, 2.06 B, 2.06 R, 128/212, 2.] R, 2.05 R,DIG. 4, 2.1 E, 410,

687,916 11/1936 -Gcrmany 128/21 R OTHER PUBLICATIONS Silcocks et al.,High-fidelity electrode/preamplifier for cardiography, Journal for theAdvancement of Biomedical Instrumentation, Vol. 5, No. 3, May, 1971Primary ExaminerRichard A. Gaudet Assistant Examiner-Lee S. Cohen [5 7ABSTRACT Apparatus is provided for sensing physiological potentials of aliving body. There is provided a first band for at least partiallyencircling a part of the living body and having a first electrodemounted thereon. The first electrode is adapted for connection to aninstrument for amplifying the physiological potentials of the livingbody. A second band is provided for at least partially encirling anotherpart of the living body and has a second and a third electrode locatedthereon. The second and third electrodes each are adapted for connectionto the instrument for amplifying the physiological potentials of theliving body.

9 Claims, 8 Drawing Figures LEFT WRIST RIGHT WRlST APPARATUS FOR SENSINGPHYSIOLOGICAL POTENTIALS BACKGROUND OF THE INVENTION 7 This inventionrelates to improvements in sensing means and electrode systems. Morespecifically, the invention relates to sensing means and electrodesystems for detecting or picking up physiological potentials of a livingbody and as such sensing means and electrode systems are used inconjunction with a recording or measuring instrument or with anamplifier, which may form a part of such an instrument, and which isused to amplify the physiological potentials. I

It may be explained here that the present method for obtaining qualityelectrocardiograms in patients requires the use of a special electrodejelly or conductive cream to minimize the contact impedance'between themetal electrodes placed in contact with the body of the patient and theskin surfaces of the patient. This special jelly or cream is usuallyadministered by a qualified In a co-pending US. application Ser. No.337,261 assigned to the same assignee as the instant application andfiled concurrently herewith there is described a monitor apparatus formonitoring electrical signals, either natural, i.e.,electrocardiographic signals, or artificial, i.e., resulting from a,heart pacer stimulating the heart of a patient, via a communicationlink. Briefly, the monitor'apparatusdisclosed in the above identifiedapplication comprises a transducer including electrode means which areused to sense the physiological signals of the patient. The transducerprocesses the sensed signals for transmission over a communication link,as for example, a standard telephone communication network. A receiver,typically located at a remote telephone station such as a cardiologistsoffice, receives the transmitted information which is thereafter used bythe cardiologist for diagnostic purposes.

The transducer of the monitor apparatus just described is usuallysitu'ated with the patient in his home and must, therefore, be operatedby the patient us ually without the assistance of a trained physician ortechnician. To this end, the transducer of the above identifiedapplication utilizes a pair of stretch arm band electrodeswhich can beutilized quite easily by the patient without assistance.

SUMMARY oF THE INVENTION technician.

Another object of the invention is to provide an improved sensing meansand electrode system which allows the patient to substantiallycompletely relax while monitoring of the physiological potentials of thepatient is effected.

tials of the patient without the aid of a physician or Briefly, thepresent invention achieves the foregoing objects by providing apparatusfor sensing physiological potentials of a living body. The apparatuscomprises: a first band for at least partially encircling a part of theliving body and having a first electrode located thereon, the firstelectrode being adapted for connection to an instrument for amplifyingthe physiological potentials of the living body; and a second hand forat least partially encircling another part of the living body and havinga second and a third electrode located thereon, the second andthirdelectrodes each being adapted for connection to the instrument foramplifying the physiological potentials of the living body.

The invention will be fully and comprehensively understood with otherobjects and advantages which will become subsequently apparent as thedetails of construction and operation thereof are more fully hereinafterdescribed and claimed.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 diagrammatically"illustrate prior art electrode systems and are useful to explainpossible problems associated with their use;

FIG. 3 is a diagrammatic illustration of the modification to one of thetwo wrist band electrodes in accordance with the invention to facilitatethe three electrode configuration of FIG. 2;

FIGS. 4, 5, and 6 show an actual implementation of the stretch wristband electrode system in accordance with the invention; and

FIGS. 7 and 8 diagrammatically illustrate modifications to the electrodesystem of FIGS. 3-6 in accordance with the invention.

DESCRIPTION OF THE PREFERRED A EMBODIMENTS the skin surfaces of thepatient during a lead 1 ECG A measurement using a two input terminalamplifier 22.

The amplifier 22 has input terminals 24 and 26 between whichphysiological voltage signals are sensed and a pair of output terminals28 and 30 between which the amplified physiological voltages appear orwhere voltage measurements are taken, as for example, cardiographicsignals (E Note that terminal 26 and terminal 30 are electricallyidentical. The effect of common mode voltages on the quality ofmeasurements will now be described. A common mode voltage (E may becharacterized as that voltage that exists between the chassis of themeasuring instrument, that is, the amplifier, and the patient. I I

Assume the following typical values for the parameters in FIG. 1: I

2, (Skin to electrode impedance utilizing a =l000 ohms conductive creambetween electrodes l8 and 20 and the skin of the patient) -Continued Z(amplifier input impedance) =l megohm Z (impedance between amplifierchassis =l000 megohm and patient) E (common mode voltage between =lvolts amplifier chassis and patient) E (cardiac voltage measured between=2 millivolts amplifier output terminals 28 and 30) The percentage errorin voltage measurement E caused by the input impedance Z, of theamplifier 22 in given approximately by the following formula (1):

Percent Error due to Z,-,, i 2 22 /2, Z X I00 Substituting the abovevalues in formula (1) provides a percentage error in the voltagemeasurement of E of approximately 0.2 percent or 0.004 millivolts.

The percentage error in voltage measurements of E caused by the commonmode voltage E is given Substituting the above values in formula (2)provides a percentage error in the voltage measurement of E ofapproximately 0.5 percent or 0.01 millivolts.

Consider now the situation if no conductive cream were used to reducethe impedance of Z,. Typically Z, would increase to 100,000 ohms andpossibly as high as 1 megohm. With Z, being equal to l megohm, thepercentage error caused by the input impedance Z,-,, of the amplifier 22utilizing formula (1) would now be approximately 67 percent or 1.34millivolts. This error could be reduced, however, bysimply increasingthe input impedance Z to 1,000 megohm which is easily obtainableutilizing a Field Effect Transistor (F ET) amplifier.

But with Z, equal to l megohm, the percentage error in voltagemeasurement of E caused by the common mode voltage E utilizing formula(2) would now be approximately 500 percent or millivolts. This lattererror cannot be'mitigated by increasing the impedance Z of amplifier 22.

However, by utilizing a three terminal input amplifier 31, as depictedin FIG. 2, having a positive input terminal 32, a negative inputterminal 34 and a signal ground terminal 36, with the amplifier 31signal ground terminal 36 connected to, for example, the right ankle ofthe patient via an electrode-37, a reduction in error proportional tothe common mode rejection capability of the amplifier 31 is realized.Assume now, however, that the interface impedance Z, between the rightankle electrode 37 and the right ankle is also 1 megohm, therefore, thecommon mode percentage error in voltage measurement of E would be 10millivolts as before. Now, however, the amplifiers common mode rejectioncapability, typically 60 db or greater will reduce this percentage errorby 60 db, or by a factor of 1,000 to 0.01 millivolts. Thus, theelectrode 37, commonly called an indifferent electrode, is to physicallyand electrically connect the signal ground terminal 36 of amplifier 31to the patient so as to reduce the common mode voltage existing betweenthe patient and the amplifier 31.

The impracticability of using a three electrode system configuration asdepicted in FIG. 2 with an unaided patient is obvious. The sensing meansor electrode system in accordance with the invention acquires 5 the sameperformance capability of the three discreet electrode configuration ofFIG. 2 using only two discreet electrodes.

FIG. 3 is a diagrammatic illustration of the modification to one of thetwo electrodes 18 and20 in accordance with the invention, to facilitatethe three electrode configuration of FIG. 2. This modification to one ofthe electrodes l8 and 20 provides two independent connections, one forthe amplifier negative input terminal 34 and one for the amplifiersignal ground terminal 36.

There is diagrammatically shown in FIG. 3, a shielded cable 40interconnecting the left wrist of the patient to the positive inputterminal 32 of amplifier 31 and a second shielded cable 42interconnecting the right wrist of the patient to the negative inputterminal 34 of the amplifier 31. The shielded cables 40 and 42 eachcomprise an inner electrical conductor 62 and a braided outer electricalconductor 64 which are insulated from one another. It will be noted thatthe braided conductors 64 of shielded cables 40 and 42 areinterconnected by lead wire 44 and that each of them are in turnconnected to the signal ground terminal 36 of amplifier 30 via lead 37.

The electrodes 18 and 20 are shown in FIG. 3 in the form of arm or wristbands and each comprises a metallic stretch band similar to watch bandhaving its opposite ends interconnected by an electrode assembly 52. Thewrist or arm bands 18 and 20 and assemblies 52 are each arranged forcontact with the skin surfaces of the arms or wrists of the patient.Each assembly 52 comprises an upper metallic plate portion 54 and alower metallic plate portion 56. It will be noted, however, that theelectrode assembly 52 of arm or wrist band 20 differs slightly from thatof arm or wrist band 18. The electrode assembly 52 of arm or wrist band20 is provided with an opening in the upper metallic plate 54 andinterposed between the upper plate 54 and the lower plate 56 is a memberor piece of electrically insulating material 58 which is also providedwith an opening 60 therethrough. The insulating material 58 is notpresent in arm or wrist band 18 and the upper and lower portions 54 and56, respectively, are physically and electrically connected to eachother and to the stretch band 50.

As shown in FIG. 3, the braided outer conductor 64 of shielded cable 40is not electrically connected to the stretch band 50 nor to theelectrode assembly 52 and only the inner electrical conductor 62 iselectrically connected to the electrode assembly 52 and thus to thestretch band 50. However, the braided outer conductor 64 of shieldedcable 42 is electrically connected via lead 66 tothe stretch band 50 andthe inner electrical conductor 62 is electrically connected to the lowermetallic plate 56. With such an arrangement, at the right arm or wristof the patient, there is in effect two separate electrical connectionsbetween the amplifier 31 and right wrist of the patient, namely, anelectrical connection is made between the input terminal 34 and theright arm or wrist of the patient via conductor 62 and lower plate 56 ofelectrode assembly 52, and another electrical connection is made betweenthe signal ground terminal 36 of amplifier 31 and the right arm or wristof the patient via lead 37, braided conductor 64,

lead 66, upper plate 54, and stretch band 50. Thus, the requirement fora separate right ankle electrode as depicted in FIG. 2, which isnormally required in a lead l ECG, is eliminated because the electricalconnection between the signal ground terminal 36 of amplifier 31 and theright'arm or wrist of the patient via lead 37, braided conductor 64,lead 66, upper plate 54, and stretch band 50 is electrically equivalentto the indifferent electrode (electrode 37) connection of FIG. 2.

Referring now to FIGS. 4, 5, and 6, there is shown an actualimplementation of the stretch arm or wrist band electrode system inaccordance with the invention. Each of the arm or wrist band electrodes18 and are constructed identically except for an electrical connectionfor the indifferent electrode and therefore, only the arm or wrist bandelectrode 20 is illustrated in FIGS. 4, 5, and 6.

In FIGS. 4, 5, and 6, the arm or wrist electrode is again showngenerally at 20; the stretch band isshown at 50; the shielded cable at42; the inner conductor of the shielded cable at 62 which terminates atone end in an amplifierconnector 70, and at the opposite end in a lugconnector 71; the outer braided conductor at 64 which terminates at oneend in an amplifier connector 72 and at the opposite end in a lugconnector 73; and the electrode assembly generally at 52 comprising theupper metallic plate 54, the lower metallic plate 56 and the insulationmaterial as block 58. The upper plate 54 is fastened to the insulatingblock 58 at its upper portion by means of screws 74 and 75. Lower plate56 is fastened to insulation block 58 at its lower portion by means of athreaded pin 76 formed with the plate 56or welded thereto, and a nut 78.Interposed between nut 78 and the surface 80 of insulation material 58is a metallic lock washer 81 and an electrical connector 82 onto whichlug connector 71 is snapped or otherwise secured. Another metallic lockwasher 83 and an electrical connector 84 is shown interposed between theupper plate 54 and the surfaces 85 of a recessed portion 86 provided inthe left side of the insulation material 58 as viewed in FIGS. 5 and 6.The connector 72 of braided conductor 64 is snapped onto orotherwisesecured to electrical connector 84.

As stated above, the arm or wrist electrodes 18 and 20 are identical,however, in the arm or wrist electrode 18 the braided conductor 64 iscut off as at point 88 in FIG. 4 and, therefore, is not connected to theelectrical connector 84. In fact, the electrical connector 84 is notpresent or utilized in the arm or wrist electrode 18.

From the foregoing it will be understood, that the arm or wristelectrode described with reference to FIGS. 4, 5, and 6, is an actualimplementation of the arm or wrist electrodes 18 and 20 described withreference to FIG. 3.

Referring now to FIG. 7, there is diagrammatically illustrated amodification to the electrode system of the invention wherein a pair ofresistors R and R, are eIec-- trically connected between the shieldedconductors 64 and the stretch'bands 50. While the insulation material58, the wrist bands 50 and the shielded cable 42 are illustratedsomewhat differently in FIG. 7 than in FIGS. 3-6, they are electricallyequivalent to those. shown in FIGS. 3-6. Also, in FIG. 7, both arm orwrist band electrodes are identical, that is, they are both identical tothat shown at 20 in FIG. 3.

The values of the resistors R and R need not necessarily be the same butthe sum of the two must be large compared with the impedance of thepatient between his right arm and left arm, as for example, R plus Rmust be greater than 500 ohms which typically represents the body fluidimpedance between the right arm and left arm of the patient neglectingcontact impedance (2,) between the electrodes and the skin surfaces ofthe patients body. However, the sum of R, and R must be low enough to beeffective to reduce the common mode voltage. Typically R plus R shouldbe in the range from about 1,000 ohms to about 20,000 ohms.

Referring now to FIG. 8, there is diagrammatically illustrated amodification of the electrode system of the invention shown in FIG. 7wherein the pair of resistors R and R are electrically connected betweenthe braided conductors 64 of shielded cable 42 and the stretch wristbands 50 at the amplifier end via signal ground terminal 36 and leadsand 82 connected, respectively, between the braidedconductors 64 of theleft and right stretch bands 50. Electrically, the embodiment shown inFIG. 8 is the equivalent of that shown in FIG. 7.

The advantages of the embodiments of the invention shown in FIGS; 7 and8 are that should anyone of the ground connections between the patientand the amplifier 31 fail or become reduced because of corrosion or dirtor other failure, as for example, one of the arm or wrist stretch bands50 not making effective contact, then the alternative arm or wristelectrode 18 or 20 ground connection will function to provide analternate ground path or connection between the patient and theamplifier 31.

It should also be pointed out here that both R, and R may be replaced bya short circuit if a sufficient resistance is present due to the contactimpedance between the stretch bands 50 and the skin surfaces of thepatient, but, since the contact resistance or impedance between thestretch bands 50 and the skin surfaces of the patient cannot be assuredof being of any given value, the use of resistors R and R is preferred.

From the foregoing it will be understood to those skilled in the artthat the invention in its broadest aspects comprises apparatus forsensing or picking up physiological potentials of a living body whichwhen used in conjunction with an instrument for amplifying or measuringthese potentials provides three independent electrical connectionsbetween the living body and the instrument utilized, but does soutilizing only two discreet sensing or pick-up means. Further while thewrist or arm electrodes 18 and 20 including the stretch bands 50 and theelectrode assemblies 52 have thus far been described as metallic, ifdesired, they may be completely or partially be fabricated of anysuitable electrically conductive material, as for example, anelectrically conductive plastic material or carbon. Also, the stretchbands 50 of wrist or arm electrodes 18 and 20 may be in the form offlexible bracelets for only partially encircling the wrists or arms ofthe patient, and, for that matter, are not restricted for use on thearms or wrists of the living body but may be constructed and arranged towholly or partially encircle any appropriate part of the living body. Asfor the stretch bands 50 themselves, they may actually be fabricated ofan electrically insulating material such as a rubber band for completelyencircling a body part or a rubber bracelet for only partiallyencircling the body part. In these latter situations one of the rubberbands or bracelets, i.e., the equivalent of 18, would have anelectrically conductive electrode, such as the electrode 52, mountedthereon for contact with the skin surfaces of the living body and theelectrode would be provided with any suitable electrical connector forelectrical connection to the instrument being utilized; in the case ofthe other rubber band or bracelet, i.e., the equivalent of 20, therewould be mounted thereon for contact with the skin surfaces of theliving body, two spaced apart electrically conductive electrodes, suchas 56 and each of the electrodes would be provided with any suitableelectrical connector for electrical connection via electricalconductors, such as shielded cables 40 or 42, appropriately connected tothe instrument being utilized. Again, in these latter situations withboth arm or wrist band electrodes 18 and 20 being identical, theresistors R and R may be utilized as they are described with referenceto FIGS. 7 and 8.

Also from the foregoing, it will be understood that with respect to theelectrode system, we have provided an electrode system wherein a patientcan record his own ECG without the aid of a physician or technician. Theelectrode system of the invention is especially useful with the monitorapparatus described in the above identified co-pending application. Theelectrode system of the invention permits the patient to completelyrelax while physiological measurements are being taken as there isnothing that the patient must hold or grasp during the measurementprocess. Thus, much of the electrical noise introduced into themeasurement process due to the normal requirement that a patient graspelectrodes, which noise emanates from muscle tension of the patient, iseliminated. Also, use of the electrode system of the invention permitsthe patient freedom of movement which may be required for obtainingother measurements.

While we have herein described and shown illustrative embodiments of ourinvention, it is to be understood that the invention is not limitedthereto, but may comprehend other constructions, arrangements of parts,details and features without department from the spirit of theinvention.

Having thus described our invention, we claim:

'1. An electrode system for use with an instrument constructed andarranged for the measurement of physiological potentials of a patientwherein the instrument has at least three input terminals, one being apositive input terminal, one being a negative input terminal and onebeing a signal ground terminal, the electrode system comprising:

a. a first band for encircling a part of the body of the patient andhaving a first electrode located thereon;

b. a first electrical conductor having opposite ends,

one end of the first electrical conductor being electrically connectedto the first electrode and the opposite end thereof being connected tothe positive input terminal of the instrument;

c. a second band for encircling another part of the body of the patientand having a second and third electrode located thereon; and

d. second and third electrical conductors, each having opposite ends,one end of the second electrical conductor being electrically connectedto the second electrode and the opposite end thereof being electricallyconnected to the negative input terminal of the instrument, one end ofthe third electrical conductor being electrically connected to the thirdelectrode and the opposite end thereof being electrically connected tothe signal ground terminal of the instrument.

2. Apparatus as defined in claim 1 wherein the first band is fabricatedof electrically conductive material with the first electrode beingelectrically connected thereto.

3. Apparatus as defined in claim 1 wherein the second band is fabricatedof electrically conductive material with the second electrode beingelectrically connected thereto, a piece of electrically insulatingmaterial, the third electrode being electrically insulated from thesecond band by the piece of electrically insulating material.

4. An electrode system for use with an amplifier adapted for themeasurement of physiological potentials of a patient wherein theamplifier has three input terminals, one being a positive inputterminal, one being a negative input terminal and one being a signalground terminal, the electrode system comprising:

a. a first conductive band having its opposite ends electricallyinterconnected, the first conductive band being constructed and arrangedfor physical.

and electrical contact with the skin surfaces of a limb of the patient;

b. a first electrical conductor having opposite ends,

one end of the first electrical conductor being electrically connectedto the first conductive band and the opposite end thereof being (for)electrically (interconnecting the first conductive band with the)connected to the positive input terminal of the amplifier,

. a second conductive band having its opposite ends interconnected by anelectrode assembly, the second conductive band and the electrodeassembly each being constructed and arranged for physical and electricalcontact with the skin surfaces of a limb of the patient, the electrodeassembly comprising:

i. an upper conductive plate:

ii. a lower conductive plate; and

iii. a member of electrically insulating material interposed between theupper and lower conductive plates; the upper conductive plate of theelectrode assembly being electrically connected to the second conductiveband.

d. a second electrical conductor having opposite ends, one end of thesecond electrical conductor being electrically connected to the lowerconductive plate and the opposite end thereof being (for) electrically(interconnecting the lower conductive plate) connected to the negativeinput terminal of the amplifier; and

. a third electrical conductor having opposite ends, one end of thethird electrical conductor being electrically connected to the upperconductive plate and the opposite end thereof being (for) electrically(interconnecting the upper conductive plate) connected to the signalground terminal of the amplifier.

5. An electrode system as defined in claim 4 wherein the firstconductive band has its opposite ends electrically interconnected by afirst electrode assembly comprising:

i. an upper metallic plate; and ii. a lower metallic plate, the upperand lower metallic plates being electrically connected together.

6. An electrode system for use with an amplifier constructed andarranged for the amplification of physiological potentials of a patientwherein the amplifier has three input terminals, one being a positiveinput terminal, one being a negative input terminal and one being asignal ground terminal, the electrode system comprisa. a first metallicstretch band having its opposite ends interconnected by a firstelectrode assembly,

the first metallic stretch band and at least one portion of the firstelectrode assembly being constructed and arranged for physical andelectrical contact with the skin surfaces of a limb of the patient, thefirst electrode assembly comprising:

i. a first upper metallic plate portion;

ii. a first lower metallic plate portion; and

iii. a first block of electrically insulating material interposedbetween the first upper and lower metallic plate portions, the firstupper metallic plate portion being secured to an upper portion of theblock of insulating material and the first lower metallic plate portionbeing secured to a lower portion of the first block of insulatingmaterial, the first upper metallic plate portion being physically andelectrically connected to the opposite ends of the first metallicstretch band;

b. a first cable having first and second electrical conductors, thefirst and second electrical conductors being insulated from one another,the first electrical conductor being electrically connected at one endthereof to the first lower metallic plate portion and the opposite endthereof being (constructed and arranged for electrical connection)electrically connected to the positive input terminal of the amplifier,

. a second metallic stretch band having its opposite ends interconnectedby a second electrode assembly, the second metallic stretch band and atleast one portion of the second electrode assembly being constructed andarranged for physical and electrical contact with the skin surfaces of alimb of the patient, the second electrode assembly. comprising:

i. a second upper metallic plate portion;

ii. a second lower metallic plate portion; and

iii. a second block of electrically insulating material interposedbetween the second upper and lower metallic plate portions, the secondupper metallic plate being secured to an upper portion of the secondblock of insulating material and the second lower metallic plate portionbeing secured to a lower portion of the second block of insulatingmaterial, the second upper metallic plate portion being physically andelectrically connected to the opposite ends of the second metallicstretch band;

d. a second cable having first and second electrical conductors, thefirst and second electrical conductors of the second cable beinginsulated from one another, the first electrical conductor of the secondcable being electrically connected at one end thereof to the secondlower metallic plate portion and the opposite end thereof being(constructed and arranged for electrical connection) electricallyconnected to the negative input terminal of the amplifier, the secondelectrical conductor of the second cable being electrically connected atone end thereof to the second metallic stretch band and the opposite endthereof being (constructed and arranged for electrical connection)electrically connected to the signal ground terminal of the amplifier.

7. An electrode system as defined in claim 6 wherein the secondelectrical conductor of the first cable is electrically connected at oneend thereof to the first metallic stretch band and is electricallyconnected at its opposite end to the signal ground terminal of theamplifier.

8. An electrode system as defined in claim 7 wherein the secondelectrical conductor of the first cable is electrically connected atsaid one end thereof to the first metallic stretch band via a firstresistor and wherein the second electrical conductor of the second cableiselectrically connected at said one end thereof to the second metallicstretch band via a second resistor.

9. An electrode system as defined in claim 7 including a first resistorconnected to the said opposite end of the second electrical conductor ofthe first cable, wherein the said opposite end of the second electricalconductor of the first cable is electrically connected to the signalground terminal of the amplifier via said first resistor, and a secondresistor connected to the said opposite end of the second electricalconductor of the second cable, wherein the said opposite end of thesecond electrical conductor of the second cable is electricallyconnected to the signal ground terminal of the amplifier via said secondresistor.

1. An electrode system for use with an instrument constructed andarranged for the measurement of physiological potentials of a patientwherein the instrument has at least three input terminals, one being apositive input terminal, one being a negative input terminal and onebeing a signal ground terminal, the electrode system comprising: a. afirst band for encircling a part of the body of the patient and having afirst electrode located thereon; b. a first electrical conductor havingopposite ends, one end of the first electrical conductor beingelectrically connected to the first electrode and the opposite endthereof being connected to the positive input terminal of theinstrument; c. a second band for encircling another part of the body ofthe patient and having a second and third electrode located thereon; andd. second and third electrical conductors, each having opposite ends,one end of the second electrical conductor being electrically connectedto the second electrode and the opposite end thereof being electricallyconnected to the negative input terminal of the instrument, one end ofthe third electrical conductor being electrically connected to the thirdelectrode and the opposite end thereof being electrically connected tothe signal ground terminal of the instrument.
 2. Apparatus as defined inclaim 1 wherein the first band is fabricated of electrically conductivematerial with the first electrode being electrically connected thereto.3. Apparatus as defined in claim 1 wherein the second band is fabricatedof electrically conductive material with the second electrode beingelectrically connected thereto, a piece of electrically insulatingmaterial, the third electrode being electrically insulated from thesecond band by the piece of electrically insulating material.
 4. Anelectrode system for use with an amplifier adapted for the measurementof physiological potentials of a patient wherein the amplifier has threeinput terminals, one being a positive input terminal, one being anegative input terminal and one being a signal ground terminal, theelectrode system comprising: a. a first conductive band having itsopposite ends electrically interconnected, the first conductive bandbeing constructed and arranged for physical and electrical contact withthe skin surfaces of a limb of the patient; b. a first electricalconductor having opposite ends, one end of the first electricalconductor being electrically connected to the first conductive band andthe opposite end thereof being (for) electrically (interconnecting thefirst conductive band with the) connected to the positive input terminalof the amplifier, c. a second conductive band having its opposite endsinterconnected by an electrode assembly, the second conductive band andthe electrode assembly each being constructed and arranged for physicaland electrical contact with the skin surfaces of a limb of the patient,the electrode assembly comprising: i. an upper conductive plate: ii. alower conductive plate; and iii. a member of electrically insulatingmaterial interposed between the upper and lower conductive plates; theupper conductive plate of the electrode assembly being electricallyconnected to the second conductive band. d. a second electricalconductor having opposite ends, one end of the second electricalconductor being electrically connected to the lower conductive plate andthe opposite end thereof being (for) electrically (interconnecting thelower conductive plate) connected to the negative input terminal of theamplifier; and e. a third electrical conductor having opposite ends, oneend of the third electrical conductor being electrically connected tothe upper conductive plate and the oPposite end thereof being (for)electrically (interconnecting the upper conductive plate) connected tothe signal ground terminal of the amplifier.
 5. An electrode system asdefined in claim 4 wherein the first conductive band has its oppositeends electrically interconnected by a first electrode assemblycomprising: i. an upper metallic plate; and ii. a lower metallic plate,the upper and lower metallic plates being electrically connectedtogether.
 6. An electrode system for use with an amplifier constructedand arranged for the amplification of physiological potentials of apatient wherein the amplifier has three input terminals, one being apositive input terminal, one being a negative input terminal and onebeing a signal ground terminal, the electrode system comprising: a. afirst metallic stretch band having its opposite ends interconnected by afirst electrode assembly, the first metallic stretch band and at leastone portion of the first electrode assembly being constructed andarranged for physical and electrical contact with the skin surfaces of alimb of the patient, the first electrode assembly comprising: i. a firstupper metallic plate portion; ii. a first lower metallic plate portion;and iii. a first block of electrically insulating material interposedbetween the first upper and lower metallic plate portions, the firstupper metallic plate portion being secured to an upper portion of theblock of insulating material and the first lower metallic plate portionbeing secured to a lower portion of the first block of insulatingmaterial, the first upper metallic plate portion being physically andelectrically connected to the opposite ends of the first metallicstretch band; b. a first cable having first and second electricalconductors, the first and second electrical conductors being insulatedfrom one another, the first electrical conductor being electricallyconnected at one end thereof to the first lower metallic plate portionand the opposite end thereof being (constructed and arranged forelectrical connection) electrically connected to the positive inputterminal of the amplifier, c. a second metallic stretch band having itsopposite ends interconnected by a second electrode assembly, the secondmetallic stretch band and at least one portion of the second electrodeassembly being constructed and arranged for physical and electricalcontact with the skin surfaces of a limb of the patient, the secondelectrode assembly comprising: i. a second upper metallic plate portion;ii. a second lower metallic plate portion; and iii. a second block ofelectrically insulating material interposed between the second upper andlower metallic plate portions, the second upper metallic plate beingsecured to an upper portion of the second block of insulating materialand the second lower metallic plate portion being secured to a lowerportion of the second block of insulating material, the second uppermetallic plate portion being physically and electrically connected tothe opposite ends of the second metallic stretch band; d. a second cablehaving first and second electrical conductors, the first and secondelectrical conductors of the second cable being insulated from oneanother, the first electrical conductor of the second cable beingelectrically connected at one end thereof to the second lower metallicplate portion and the opposite end thereof being (constructed andarranged for electrical connection) electrically connected to thenegative input terminal of the amplifier, the second electricalconductor of the second cable being electrically connected at one endthereof to the second metallic stretch band and the opposite end thereofbeing (constructed and arranged for electrical connection) electricallyconnected to the signal ground terminal of the amplifier.
 7. Anelectrode system as defined in claim 6 wherein the second electricalconductor of the first cable is electrically cOnnected at one endthereof to the first metallic stretch band and is electrically connectedat its opposite end to the signal ground terminal of the amplifier. 8.An electrode system as defined in claim 7 wherein the second electricalconductor of the first cable is electrically connected at said one endthereof to the first metallic stretch band via a first resistor andwherein the second electrical conductor of the second cable iselectrically connected at said one end thereof to the second metallicstretch band via a second resistor.
 9. An electrode system as defined inclaim 7 including a first resistor connected to the said opposite end ofthe second electrical conductor of the first cable, wherein the saidopposite end of the second electrical conductor of the first cable iselectrically connected to the signal ground terminal of the amplifiervia said first resistor, and a second resistor connected to the saidopposite end of the second electrical conductor of the second cable,wherein the said opposite end of the second electrical conductor of thesecond cable is electrically connected to the signal ground terminal ofthe amplifier via said second resistor.